The appointment of Ruddock is a significant coup for the Ireland Under-20 side who won last season's U-20 Six Nations Championship.
Ruddock has an impressive coaching background at both club and international level and as a player he represented Swansea and Wales 'B' before injury cut his playing days short.
His coaching career began following that retirement, and his strong ties with Ireland started with a spell as coach of Dublin club side Bective Rangers before he returned to coach Swansea for six seasons.
He then came back to Ireland to take the position of Leinster director of rugby in 1997 where he remained until 2000 when he moved to Ebbw Vale as coach, assisting with the Wales 'A' squad.
He then coached the Newport Gwent Dragons before taking the post of Wales national coach in 2004, leading them to an RBS Six Nations Championship Grand Slam in 2005.
He left that role in 2006 and has been coaching English club side Worcester until this summer.
Ruddock's links with Ireland go beyond his own coaching career as his mother originally comes from County Clare and his wife hails from Dublin. Both his sons, Ciaran and Rhys, have also played for Ireland at Under-20 level.
Rhys captained the U-20s to the 2010 Six Nations title and then finished the season by winning his first senior cap for Ireland against Australia during the summer tour in June.
Mike Ruddock will concentrate purely on the coaching of the Ireland Under-20 squad, which will allow IRFU High Performance Manager Allen Clarke to focus fully on the further development of the elite player pathway and programmes that have been implemented by Clarke since his appointment in 2007.
Clarke said: "It has been a fantastic honour to coach the Ireland Under-20s for the past two seasons. However it was only ever a bridging arrangement and I am really looking forward to supporting and working with Mike.
"The challenge as High Performance Manager is to ensure that our elite programmes and their delivery are world class.
"Working with our provincial structures, national age grade teams and our schools and clubs, we will look to continue to provide a continuous flow of indigenous quality players for the professional game in Ireland."
Commenting on his own appointment, Ruddock said: "The importance of this age grade level is vital and the chance to work in Irish rugby again was one I did not want to pass up on.
"Allen has made some real strides with the team, with their Championship success last season and runners-up spot the previous year a testament to this.
" I am looking forward to working very closely with him to ensure there is continuity with what I want to bring to the team and most importantly keeping the Under-20 squad as the focal point for the identification pathway for future professional players.
"The focus with any underage team is trying to develop players and also trying to add a winning culture to the ones that pass through the team each year.
"A good part of my coaching career has been spent here in Ireland and with my own personal experiences through Ciaran and Rhys playing for the Under-20s, I feel I have a good understanding of the systems and I am really looking forward to getting involved to help develop young players."
IRFU Director of Rugby Eddie Wigglesworth was also delighted with the appointment and said: "This appointment is an important and welcomed addition to the elite player pathway. The time needed to coach an Under-20 squad, in terms of selection and preparation, has increased significantly.
"With Allen Clarke doubling up his role as High Performance Manager as well as Under-20 coach, it was felt that it would be more beneficial to focus on the high performance aspect which has become more vital over the last three years.
"Mike adding his considerable coaching ability to work with Allen strengthens the overall elite player systems."
Mike Ruddock will take up his role with the IRFU at the end of August as he is currently on a family holiday and will be made available for media interviews upon his return.